Short-circuiting device



Jan. 3, 1928.

E. C. BALLMAN SHORT CIRCUITING DEVICE Filed Sept. 4, 1925 Patented Jan.3, 1928.

UNITED STATES EDWIN o. B LLMAN. or s'r. LOUIS, MISSOURI.

SHORT-CIRCUITING DEVICE.

Application filed September This invention pertains to electric motorsand more partlcularly to a device for short circuiting the commutator asis done in the starting operation of many types of commutator motors. I

The customary manner of short circuiting a commutator involves the useof a series of contactors, usually operated by centrifugal force, andarranged to contact with the com mutator segments at a predeterminedmotor speed. These cont actors connect the various commutator segmentswith a short circuiting ring. At the instant at which the commutator isshort circuited there is usually a heavy rush of current through thecontactors. This'current must pass through the point of contact betweenthe contactor and the commutator segment. The usual experience has beenthat considerable arcing takes place at these points of contact. Afternumerous operations theeffect of such arcing is to cause the commutatorsegments and the contactors' to become rough, so that a good contactisno longer possible. Accordingly the eifectiveness of the short circuitis impaired when such roughening or corrosion of the contact pointstakes place.

One of the objects of this inventionflcherefore, is to "provide a shortcircuiting device of novel construction which will obviate the troubledue to corrosionof the contact points.

Another object is to provide an auxiliary set of contactors whichwillaccomplish the make and break operations so that the main contaotorswill be relieved of the arcing.

Another object is to provide such a device which will be simple andeconomical to main ufactu're and reliable in service.

Further objects will appear from the following description taken inconnection with the accompanying drawing in which:

Figure 1.is a view partly in section of a commutator equipped with ashort circuiting device embodying this invention;

Figure 2 is a partial end view of Figure 1; and

Figures 3 and 4 are detail views illustrating the action of thecontactors.

Referring to the accompanying drawing 1 designates the motor shaft whichmay have mounted thereon in any suitable manner a commutator hub 2,carrying commutator segments 3. This maybe of any ordinary constructionwell known in the art. Mounted on the shaft 1 just in front of thecommutator is a metallic cup 4. This should be 4,'-1925. Serial no;54,456.

made of a material having high electrical conductivlty such as brass orcopper. The cup 4 is adapted not only to provide a mounting for theshort circuiting contactors as will 7 presently be described, but alsoacts as a short circuit ring to carry the inter-change of currentsbetween said contactors.

Pivoted in the ring 4 are two series of contactors, a series of maincontactors 5 and a series of auxiliary contactors 6. These contactorsare formed by punching, or other suitable operation, of wedge shapedcopper or brass similar-to that used for commutator segments. shown inFigures 1, 3 and 4 comprising a lever portion 7; a tail piece 8, asharply angled point 9, slightly rounded to form a p vot, a weight orbody portion 10 and contacting faces 11 and 12. As will be seen fromFigure 3 the main and auxiliary contactors are identical in form exceptfor the contacting portions, that of the auxiliary contacts 6 beinglonger than that'of the main contacts 5 so that the contacting face 12of each auxiliary contactor will extend beyond the contacting faces11 orthe main contactors.

,Such construction provides that the auxiliary contactors will makecontact in advance of and break contact after the main contactors.

The c-ontactors are mounted in the ring 4 In such a way that the pivots9 of the contactors fit into the corner at the bottom of the rim 13 ofsaid'ring. The contactors are assembled close together all around thecup 4 as shown in Figure 2, there being approximately three main to oneauxiliary contactor. This mounting provides that each contactor willhave a pivot at its corner 9 in the cup 4. A pressure plate 14 of.circular form and fitting over the shaft 1 so as to slide therealongengages the tail pieces of all of the contactors and is pressedthereagainst by acoil spring 15 surrounding the shaft 1.- This plateoperates to'press the contactors into the cup 4; so that their tailpieces 8 will all be forced down against the rim'of the cup so as tomaintain their con tactfaces clear of the commutator as shown in Figure3;

The assembled contactors are protected by a cup shaped cover 16 mountedon the shaft 1 and having a flange 17 extending over the contactors andtoward the commutator.

The contactors have the form The 1 half ring sections 18 fitting into anannula groove 19 in the shaft 1 and each is provided with an inwardlyprojecting car 20 extending through a notch .21 in the cover 16. Thespring 15 bears at one end against the inte rior of the cover and at itsother end against the pressure plate 14: so that this sprin not onlyprovides pressure for retracting the contactors from engagca'ient withthe commutator but also serves to re tain the cover 16 in lockingengagement with the sections 18, which not. only hold the cover 16 inplace but are themselves retained in place thereby.

in the operation of this device, when the motor is at rest, thecontactors assume the positions illustrated in Figure 3. lVhen the motoris started and attains a predetermined speed the centrifugal force ofthe body portions 10 of the contactors, acting through the leverportions 7 and the tail pieces 8 overcomes the pressure of the plate 14.hen this takes place the contactors turn on the pivots 9 so as to bringthe contacting faces 12 and 11 into engagement with the commutatorsegments 3. The auxiliary contactors make contact first at their faces12 and the arcing takes place at these contacts. Subsequently as themotor speed increases further, the main. contacts engage thecon'in'iutator segments at their faces 11. \Vhen this point has beenreached the contactors are in the positions illustrated in Figure 1.Here both series of contactors are in engagement with the commutator.However, the tail pieces 8 of the main cont actors have pushed thepressure plate 14 outwardly so as to free the tail pieces of theauxiliary contactors 6 as illustrated in Figure 1. The further action ofcentrifugal force on the auxiliary contaetor will now move them in sucha Way that the pivot point 9 slides outwardly along the rim 13 until thetail pieces again engage the plate 14. This position is shown in Figure1 During this movement the auxiliary contactors have a slight rockingmotion at their contact faces 12 so that a varying contact is obtainedat this point which assists in reducing the corrosion due to arcing. Itwill further be noted that the contact faces 11 and 12 are displacedradially with respect to one another. Accordingly they will engage thecommutator at different parts thereon. This provides that the arcing atthe face 12 will occur at a different point on the COlIlll'lUllZl-tOlthan that engaged by the faces 11.

It will be seen, therefore, that in accordance with this invention ashort circuiting device is provided in which the arcing is confined to aseries of auxiliary contactors and to a certain place on the commutatorsegments, while the main short circuiting operation is accomplished bythe main contactors which touch the commutator at a point which is notengaged by the auxiliary contactors and which is, therefore, kept cleanand uncorroded by arcing. The auxiliary contacts engage the segmentsWith a slight rolling or slipping engagement so that the roughnessproduced by arcing will be correspondingly reduced. As the contactorsare not confined circumferentially nor limited to any fixed position,the continued operation of this device will shift the contactorscircumferei'itially with re spect to the commutator so that thecorrosion due to arcing will be distributed over the entirecircumference of the con'nnutator and not confined to any one point.

'ilie device is very chetp to manufacture. it contactor may be formed bypunching from sliitable metal. The cup 4, the plate 1 1, the cover 16and the sections 18 may each be made oi suitable sheet metal formed at asingle machine operation, and therefore, very cheap. The spring 15 issubject to only slight moven'oent upon operation of the contactors and,therefore, its change in strength due to conipressfon will be slightwhile the contactors move radially outwardly, thereby ii'icreasing theforce which they exert upon the spring. Accordingly the contactors willmove positively against the spring tension, an action which is desirablein order to avoid excessive arcing. The cover 16 provides protection forthe device while at the same time aflording easy access thereto.

This construction also provides for easy accessibility, as the device iseasily disassembled by simply pushing in the cover 16 to free thesections 18 which are then removed. and the cover slipped back on theshaft. This releases the spring 15 and the plate let so as to render allthe contactors accessible for removal or replacement. The contactors arethus easily removable for cleaning the contacting surface of thecommutator.

It is obvious that various changes may be made in the details ofconstruction Without departing from the spirit of this invention; it isto be understood, therefore, that this invention is not to be limited tothe specific details shown and described.

Having thus descirbed the invention what is claimed is:

1. In an electric motor, a short-circuiting device, comprising, acommutator, a series of main contactors adapted to make contact with thecommutator segments, and a series of auxiliary contactors adapted tomake contact with the commutator se 'inents in advance of said maincontactors.

2. In an electric motor, a short-circuiting device, comprising, acommutator having segments, a series of main contactors centrifugallyoperated to contact with said segments at a predetermined motor speedand a series of auxiliary contactors centrifugally trifugally operatedto contact with said segments at a predetermined motor speed and aseries of auxiliary contactors centrifugally operated to contact withsaid segments at a difierent place on the commutator from said maincontacts.

l. In an electric motor, a short-circuiting device comprising, acommutator having segments, a series of main contactors and a series ofauxiliary contactors centrifugally operated to contact with saidsegments at a predetermined motor speed, said main and auxiliarycontactors having their contacting portions relatively displaced.

5. In an electric motor, a short dircuiting device, comprising, acommutator having segments, a series of main contactors centrifugallyoperated to contact with said segments at a predetermined motor speedand a series of auxiliary contactors centrifugally operated to contactwith said segments and to disengage said segments after said maincontactors.

6. In an electric motor, ashort-circuiting device, comprising, acommutator having segments, a series of main contactors centrifugallyoperated to contact with said segments at a predetermined motor speedand a series of auxiliary contactors centrifugally operated to contactwith said segments in advance of said main contactors and with a varyingcontact.

7. In an electric motor, a sliort-circuiting device, comprising acommutator having segments, a .series of main contactors and a series ofauxiliary contactors cent-rifugally operated to contact with saidsegments at a predetermined motor speed, a cover for said contactors,locking means for retainin said cover in place, said locking means beingadapted to be retained by said cover, and resilient means for retainingsaid cover in engagement with said locking means.

8. In an electric motor, a short-circuiting device, comprising, acommutator having segments, a series of main contactors and a series ofauxiliary contactors centrifugally operated to contact with saidsegments at a predetermined motor speed, a spring for restraining saidcontactors against the centrifugal force thereof, a cover for saidcontactors, and a loose locking element adapted to retain said cover andto be retained by said spring.

In testimony whereof I afiix my signature this 21st day of April 1925.

EDI/VIN C. BALLMAN.

